Multicolor electrostatic printing system

ABSTRACT

In an electrostatic printing system of the type wherein electroscopic powder is applied to one side of an image screen whereby it can pass through apertures arranged in the shape of an image and is carried in the shape of that image by an electric field established between the screen and a receiving substrate, there is provided an improved arrangement whereby the image can be printed in different colors on the substrate with a single exposure to the image screen.

United States Patent [72] Inventor Clyde 0. Childress Palo Alto, Calif. 21 Appl. NO. 800,427 [22] Filed Feb. 19, I969 [45] Patented June 29, 1971 l i [73] Assignec Electrostatic Printing Corporation of America San Francisco, Calif.

[54] MULTICOLOR ELECTROSTATIC PRINTING SYSTEM 4 Claims, 7 Drawing Figs.

[52] U.S.CI 101/115, 101/D1G. l3 [5 I] Int. Cl B411 15/04 [50] Field ofsearchum 101/114, 115,129,DIG.13

[56] 1 References Cited UNITED STATES PATENTS 659,535 10/1900 Lankford 101/115 X 737,945 9/1903 Lundeberg 101/115 X Ekstrom Norman l0l/ll5X Hommelm 101/115X Cantor 101/115 Zimmerman etal 101/115 Farrow.. 101/115 Leeds 10l/115X Frohbach et a1. IOl/DIG. 13 Kramer et al. 10l/D1G. 13 Childress 10l/D1G. 13 Childress et a1. 10l/D1G. 13

Primary Examiner-Edgar S. Burr Attorneys-Samuel Lindenberg and Arthur Freilich MULTICOLOR ELECTROSTATIC PRINTING SYSTEM BACKGROUND OF THE INVENTION This invention relates to electrostatic printing systems and more particularly to an improved arrangement for printing in many colors with a single exposure to the image screen.

In U.S. Pat. No. 3,081,698 there is described an electrostatic printing system wherein a screen, called an image screen, has open apertures therein which define an image, while the remaining apertures are blocked. An object or substrate upon which it is desired to print is placed on one side of the image screen. A source-of electric potential is connected between the screen and the object, if it is sufficiently conductive to establish an electric field between it and the screen, or if not, to a conductive plate placed behind the object. Electroscopic powder particles are introduced into the electric field existing between the screen and the object through the open apertures in the image screen. The electric field carries these powder particles to the object and deposits them in the form of the image. The powder image is thereafter fixed by heat or vapor or any other suitable means.

In order to print an image having more than one color, a different image screen was required to be used for each color as is required with wet printing systems. Each of these image screens would have its openings in the pattern of the particular color which is to be printed. Then, after a printing with one color and one image screen, a second image screen with a second colored ink would have to be registered with the image printed thus far, to print the second color, and so forth.

From the foregoing, it will be appreciated that while printing multicolor images with heretofore available techniques is .quite feasible, it is also troublesome. The present invention achieves multicolor image printing using a single image screen and a single exposure of an object to the image screen. The present invention is a unique arrangement for simplifying multicolor printing in an electrostatic printing system.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I illustrates a multicolor print, by way of illustration of an image which is printable with this invention.

FIGS. 2, 3 and 4 are illustrative of steps in the construction and positioning of printing powder containers in accordance with this invention.

FIG. 5 is illustrative of an assembled printer in accordance with this invention.

FIG. 6 is a cross-sectional view illustrating the operation of an embodiment of this invention.

FIG. 7 is a view illustrative of container wall arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is illustrated a four-color print, by way of example, which heretofore would have required four different exposures to four different image screens to obtain the end product. Each image screen would have openings in the form of an image for the particular color to be printed therewith. The rest of the image would be blanked out. Great care had to be taken during the printing process to insure the registration of the respective screens so that the desired multicolored image would be produced.

In accordance with this invention, and as may be seen from FIG. 3, for each different color, a container is provided having the form of the color image to be printed and containing the electroscopic ink of the color to be printed. Furthermore, the containers are assembled in the manner required to print the final colored image.

As shown in FIG. 2, initially, a layer of soft slightly resilient material 12, such as styrofoam is adhered to a rigid support 14, such as epoxy-fiberglass board. Then, the outlines 16 of the multicolor-image to be printed, are either drawn, printed, or projected on the surface of the material 12. This can be done in any suitable manner, either photographically, electrostaticly, or by light projection, or by simply sketching the image on the styrofoam.

After the sketch has been made, by using a suitable cutting tool, a cut is made into the foam down to the fiberglass layer. Thereafter, as may be seen in cross section in FIG. 4, thin shim stock 18, which may be on the order of 4 mils in thickness, is inserted into the opening made by cutting into the foam to define the respective walls of the containers, 20, 22, 24, 26

and 28 for the different colors ofink to be used in making the print. These container walls' are held upright by the foam. The placement of these cuts and divider strips are critical only when the color transition must bisect a continuous image area. It will be appreciated that in many cases the areas to appear in difierent colors will be distinct and separate pictorial or typographic elements separated by nonprinting or closed areas on the image screen. In such cases it is only necessary that the divider strip be placed at some point within the bounds of this closed area. I

The compartment-forming dividers represented in FIG. 6 maybe advantageously constructed so that the upper edge which contacts the image screen is substantially thinner than the main body of the strip, an attached strip of 2-mil-thick Mylar is suitable for this purpose. The metal base stock gives the required mechanical stability while the thin upper edge eliminates any visible blank area at the junction between the defined color areas. The divider strips may also be very finely embossed or corrugated with lines across the narrow dimension, these lines guide the angle of the required bending and shaping of the strips so that the bends are constrained to occur along lines at right angles to the length of the strip so as to easily maintain the dividers in a consistent vertical orientation relative to the horizontal screen plane.

Each container is next filled with a mixture of pigment particles, represented in FIG. 6 by the small circles 32 and by iron filings represented by the large circles 34. As is described in US. Pat. No. 3,202,092, the iron filings are selected to have a size which is larger than the screen apertures in the conductive screen 36, and the pigment particles are selected to have a size which is small enough to pass through the openings in the conductive screen without any difficulty.

After the respective containers are filled with the respective different-color powder inks as shown in FIG. 5, the image screen is brought into place and is supported touching the insulating material 30 which define the edges of the respective containers. The screen is placed over the containers in a manner so that the image-opening region is in registry with the appropriate divider strips. The result is that each differentcolor ink is retained in a container having resiliently supported walls and the image screen closing off the open end.

FIG. 6 is a cross-sectional view of FIG. 5 in conjunction with a backplate 38 and a substrate 40, such as a sheet of paper, upon which printing is to occur. A source of potential 42, is connected between the backplate and the screen such that when the switch 44 is closed, there is an electric field established thereacross. A magnet 46 is thereafter moved across the backside of the backplate 38 causing the iron filings to be lifted against the screen pushing the ink powder particles through the openings in the screen. As a result, the ink powder particles enter the electric field and are transported across to the article 40, resulting in a colored image being printed thereon. The sheet 40 can thereafter be removed and the image can be fixed by heat or any other suitable mechanism, which is well known to the art.

The conductive plate 38 should be a material which does not act as a magnetic shield. Thus, material such as aluminum may be used.

The colored image represented in FIG. 1 is of a type where the various colors of the image abut one another (and also surround one another), and care must be taken to see that the FIG. 7 is an exploded view of an image screen and containers illustrating a situation where the container walls for the most part need not follow the various color outlines of the image. An image screen 50 has image apertures representing a bird 52 of one color, the sun 54 of another color, a tree having leaves 56 of a third color, a trunk 58 of a fourth color, and the earth 60 of a fifth color. The containers for the respective colors, shown below the image screen 50, bear the same reference numerals as the images followed by the letter C.

Thus from the drawing it will be seen that there are only two locations where the container walls must follow the line between two colors. The first is the line between tree leaves and tree trunk, and the second is the line between tree trunk and ground. Otherwise, the walls of the containers can take any desired simple shape provided that the container openings are large enough to cover the respective opposite image screen areas. The pictorial information is hereprovided by the image screen.

The arrangement described lends itself to use as an interesting toy, as well as for industrial use. As a toy, different sets of containers may be provided for printing the same image with different colors. Also, individual containers may be provided which have walls shaped so that the containers represent different objects. These separate containers can then be assembled and locked on a base by suitable simple mechanical means to afford printing of a composite picture, through a nonima'ge screen-that is one having openings all over the screen.

The foregoing description of the actual printing operation, that is, the use of magnetic particles mixed with the electroscopic ink particles and the use of a magnetic field to cause the ink particles to be introduced into the electric field is substantially in accordance with the description of a technique for moving powder in an electrostatic printing system which is shown and described in US. Pat. No. 3,202,092. It will therefore be understood that any of the other systems shown therein for magnetically moving the powder which is in each of the enclosed containers of this invention, through the screen apertures into the electric field, may be employed. This includes the use of an electromagnet, instead of a pennanent magnet, and where needed, the use of a biasing magnet on the container side of the screen for drawing and holding the magnetic particles until an opposing magnetic field is used.

Another technique for causing the powder to move out of the enclosed containers through the openings in the screen into the electric field is shown in US. Pat. No. 3,218,967. This may be termed an inertial" printing technique. Here, the particles, which are mixed with the powder particles and which are larger than the apertures in the screen, are not necessarily magnetic, and preferably have some mass. Thus, in order to print, the containers and the screen are rapidly moved toward the sheet or object upon which printing is to occur, and this motion is then suddenly stopped. The inertia of the particles within the powder cause them to push powder through the screen openings into the electric field which then transfers in the form of the image onto the image receiving object.

- To replenish the powder in the containers, one obvious scheme is of course to lift the screen and fill the various containers with the various colored pigment powder particles. These ink containers may also be filled as required through normally plugged openings in the sides of the ink containers or even through the bottom of the ink containers, with the ink being introduced either using a plunger, a lead screw, or a powder cloud.

There has accordingly been described and shown herein a novel, useful and simple system for making a multicolor print,

electrostatically, with a single exposure to the image screen.

What I claim is:

I 1. A system for electrostatically printing a multicolor image on an image receiving object using a single exposure comprismg:

an image aperture screen having openings therein in the shape of a desired multicolor image, means for establishing an electric field between said screen and said image-receiving object, v

an electroscopic powder particle container associated with each color to be printed, each said electroscopic powder particle container having walls defining an opening adjacent to and at least as large as the particular portion of the image which is to be colored by the colored electroscopic powder particles within said container, the walls of each said container contacting said screen,

said walls comprising a metal material having one end terminating spaced from said screen, and

a plastic material attached to said walls and extending to said screen,

a resilient means for supporting from one end the walls of said containers to resiliently contact said screen with said plastic material, electroscopic powder particles in each said container bearing the color of the portion of the image to be printed,

said powder having a particle size smaller than the apertures of said image screen to freely pass therethrough, and

means for moving the electroscopic powder particles in each of said containers through the apertures of said screen into the electric field between said screen and image-receiving object to be carried by said field in the form of said image onto said image-receiving object.

2. A system as recited in claim 1 wherein the walls of each electroscopic powder particle container are shaped in accordance with the shape of the particular portion of the image which is to be colored by the colored ink in said container.

3. Apparatus as recited in claim I wherein said means for moving said electroscopic powder particles in each container through the image apertures of said screen includes a plurality of magnetic particles which are larger than the openings of said image screen, which are mixed with the electroscopic powder particles in each container, and

magnetic means for establishing an electric field which attracts said magnetic particles toward said image screen thereby pushing the powder particles between them and the screen through the image apertures.

4. Apparatus as recited in claim 1 wherein said resilient means for supporting said walls of said containers comprises a layer of foam material and there is a rigid layer for supporting said foam material. 

1. A system for electrostatically printing a multicolor image on an image receiving object using a single exposure comprising: an image aperture screen having openings therein in the shape of a desired multicolor image, means for establishing an electric field between said screen and said image-receiving object, an electroscopic powder particle container associated with each color to be printed, each said electroscopic powder particle container having walls defining an opening adjacent to and at least as large as the particular portion of the image which is to be colored by the colored electroscopic powder particles within said container, the walls of each said container contacting said screen, said walls comprising a metal material having one end terminating spaced from said screen, and a plastic material attached to said walls and extending to said screen, a resilient means for supporting from one end the walls of said containers to resiliently contact said screen with said plastic material, electroscopic powder particles in each said container bearing the color of the portion of the image to be printed, said powder having a particle size smaller than the apertures of said image screen to freely pass therethrough, and means for moving the electroscopic powder particles in each of said containers through the apertures of said screen into the electric field between said screen and image-receiving object to be carried by said field in the form of said image onto said image-receiving object.
 2. A system as recited in claim 1 wherein the walls of each electroscopic powder particle container are shaped in accordance with the shape of the particular portion of the image which is to be colored by the colored ink in said container.
 3. Apparatus as recited in claim 1 wherein said means for moving said electroscopic powder particles in each container through the image apertures of said screen includes a plurality of magnetic particles which aRe larger than the openings of said image screen, which are mixed with the electroscopic powder particles in each container, and magnetic means for establishing an electric field which attracts said magnetic particles toward said image screen thereby pushing the powder particles between them and the screen through the image apertures.
 4. Apparatus as recited in claim 1 wherein said resilient means for supporting said walls of said containers comprises a layer of foam material and there is a rigid layer for supporting said foam material. 